Earl - the R120's don't have the screw-in type of header pipe. It's a two-bolt flange that bolts on. This is one of the features that separates the R120 from the older 120. I used some black RTV silicone and that greatly reduced the amount of castor slime that built up around that side of the engine.
My 60-4C uses the threaded exhaust tube and it does not leak.